This invention relates to heat-shrinkable sleeves for use in splicing electrical cables and the like and, more particularly, to a novel and highly-effective method and apparatus for manufacturing such sleeves, and to sleeves made by the method and apparatus.
U.S. Pat. No. 4,446,095, issued May 1, 1984, on an invention of Katz and Zidon, discloses the most efficient method of manufacturing long lengths of heat-shrinkable sleeves heretofore known. In accordance with the invention which is the subject of that patent, a sleeve is formed around a permeable core, and the core and sleeve are advanced together in an axial direction, the leading end of the advancing sleeve being hermetically sealed. The core and sleeve pass through a heating station, thereby heating a portion of at least the sleeve, and a fluid is introduced under pressure into the core, thereby internally pressurizing the sleeve to effect a radial expansion of the heated portion thereof. The core and sleeve then pass through a cooling station, thereby cooling the expanded sleeve to stabilize it.
The core is removed from the sleeve, and the sleeve is cut to suitable lengths which are used to join electrical cables and the like. When the sleeves are heated on site, they shrink around the cable ends and help to form a permanent splice.
It is desirable to make the interior of the sleeves as smooth as possible, because of the high-voltage electrical environment in which the sleeves are used. In accordance with the prior process, one or more binders or tapes are applied over the permeable core. The binders are preferably of a high temperature resistant film or paper. The binders are removed from the sleeve together with the metallic core before the sleeve is used in joining or splicing cables.
The use of such binders renders the inside of the sleeve relatively smooth. However, because of the unevenness of the permeable core (which may be a stranded conductor, for example) and ridge lines where successive layers of the binder overlap, the interior of the sleeve cannot be made perfectly smooth by the prior process.
The problem is exacerbated by the tendency of the compound to work its way between adjacent layers of the binder under the high pressures employed in the process of manufacturing the sleeve. The irregularities or discontinuities of the inner surface of the sleeve can give rise to cracks in the sleeve when it is expanded. At a minimum, some additional processing (machining) is required before the sleeves can be utilized.